The amendment would give the attorney general the authority to block the sale of guns or explosives to known or suspected terrorists, if the attorney general has a reasonable belief that the weapons would be used in connection with terrorism. The amendment was modified from legislation introduced in February 2015 to ensure it adheres to Senate rules for amendments added to appropriations bills.

The amendment also includes language proposed by Senators Patrick Leahy (D-Vt.) and Bill Nelson (D-Florida) to ensure that anyone who has been the subject of a federal terrorism investigation in the past five years would be automatically flagged within the existing background check system for further review by the Justice Department.

“In light of the worst mass shooting in our nation’s history, the dangerous loophole in our laws that allows known or suspected terrorists to legally purchase guns has again been exposed. We must act to close this loophole,” said Senator Feinstein. “Over the past decade, 91 percent of individuals who are known or suspected terrorists passed background checks, showing this is a pervasive problem. My amendment would simply allow the attorney general to block gun sales to these individuals and closing this loophole is the least we could do to reduce the risk of terrorist attacks in our country. I continue to work with my colleagues in hopes of reaching a compromise that can pass the Senate.”

Under current law, individuals who are known or suspected terrorists and do not fall into the one of the nine prohibited purchaser categories can legally purchase weapons. While the FBI is notified when individuals on the terrorist watch list apply for a background check through the National Instant Criminal Background Check system, it does not have the authority to block the sale.

According to the GAO, between February 2004 and December 2015, known or suspected terrorists initiated a background check to purchase a weapon 2,477 times—they successfully passed that check 2,265 times, or 91 percent.